The present invention relates to an air conditioner that controls the internal temperature, oxygen partial pressure and pressure of aircraft, including fixed-wing aircraft and rotating-wing aircraft and that supplies air of reduced oxygen concentration to the fuel system.
As air conditioners in aircraft, conventionally air cycle cooling devices are chiefly employed in which temperature-adjusted and pressure-adjusted cooled air is obtained by using a radial compressor to perform adiabatic compression of extracted air compressed in a compression section of an engine after subjecting the air to heat exchanging with external air for cooling, and by using an expansion turbine to perform adiabatic expansion of the air after subjecting the adiabatic compressed air to heat exchanging with external air for cooling.
Some military aircraft are provided with an OBIGGS (on board inert gas generation system) whereby nitrogen gas or air of elevated nitrogen concentration is injected into the fuel tank in order to prevent explosion in the event of the fuel tank being hit during a mission. Also, accident investigations of civil aircraft in recent years have revealed occurrences of fire when sparks generated from on-board wiring etc have ignited a mixture of air and fuel vapor accumulated in the space within fuel tanks. In order to prevent such fires, adoption of the above OBIGGS in civil aircraft is being studied.
This OBIGGS comprises an air separation section having a function of separating air constituents. In one type of air separation section, a selectively permeable membrane is employed whose permeability for nitrogen is higher than its permeability for oxygen. Nitrogen-enriched gas is generated by introducing air extracted from the engine to this selectively permeable membrane.
In the conventional aircraft air conditioner shown in FIG. 14, air extracted from engine 101 is cooled by a heat exchanger called a pre-cooler 102 before being practically adiabatically compressed by a radial compressor 103; the air which has thereby been raised in temperature is cooled by a heat exchanger called a main cooler 104 and practically adiabatically expanded by expansion turbine 105. Cooled air is thereby obtained. In this pre-cooler 102 and main cooler 104, cooling is performed by external air passing through ram air flow path 109. The expansion work of this expansion turbine 105 is utilized as compressive power by being transmitted to compressor 103 through shaft 106. It should be noted that when the aircraft is on the ground or in low-level flight, the external air temperature is high and the moisture content of the air is high, so when expansion takes place in expansion turbine 105, moisture in the air condenses and a mist of water droplets is formed. A water separator 107 is therefore arranged downstream of expansion turbine 105 to capture the moisture. Cabin cooling is performed by supplying the cooled air that has passed through this water separator 107 to the interior of cabin 108, including the cockpit space of the aircraft. If the engine is stopped while the aircraft is on the ground, it is arranged to be possible to supply extracted air from a high-pressure air supply unit such as an auxiliary engine called an auxiliary power unit, instead of engine 101, to the air conditioner.
In order to perform cabin heating at high altitude etc, a bypass air flow path 111 is provided to feed air extracted from engine 101 into cabin 108; this bypass air flow path 111 is opened/closed by means of a hot-air modulating valve 112. Some of the extracted air is fed to a mixing duct 113 arranged downstream of water separator 107 instead of being cooled by the air cycle cooling device constituted by compressor 103 and expansion turbine 105, by opening this hot-air modulating valve 112. In this mixing duct 113, extracted air cooled by the air cycle cooling device and extracted air that has not been cooled are mixed. Air of a suitable temperature is thus obtained by adjusting the degree of opening of hot-air modulating valve 112. Cabin heating can be performed by supplying this air of suitable temperature into cabin 108. When cruising at high altitude, the ram air flow path 109 is throttled, so the air extracted from engine 101 is kept in a moderately high temperature since it is not excessively cooled in pre-cooler 102 or main cooler 104. The air within this cabin 108 is discharged directly into the space 114 outside the fuselage through pressure reducing valve 110 in an amount corresponding to the difference obtained by subtracting the amount of leakage from the fuselage from the amount supplied by the air conditioner.
The conventional OBIGGS is provided with an air separation section 116 independent of the air cycle cooling device constituted by the compressor 103 and the expansion turbine 105. Specifically, a branch air flow path 111a is provided so that the extracted air passing through the pre-cooler 102 is branched before being fed into the air cycle cooling device, and an air separating section 116 is provided in this branch air flow path 111a. This air separating section 116 is constituted by covering a selectively permeable membrane 116a comprising a large number of hollow fibers with a housing 116b. The permeability for nitrogen (N2) and carbon dioxide (CO2) in the air of this selectively permeable membrane 116a is made higher than its permeability for oxygen (O2). The extracted air of engine 101 is separated into nitrogen-enriched gas passing through this selectively permeable membrane 116a and the remainder, oxygen-concentrated air. The nitrogen separating ability of this selectively permeable membrane 116a varies in accordance with the extracted air pressure. The nitrogen-enriched gas is supplied into a fuel peripheral region 115 such as the interior of the fuel tank or fuel pipe setting region, and the remainder of the gas that is supplied to the region 115 more than needed is discharged to the space 114 outside the fuselage through a discharge flow path. The oxygen-concentrated air that has not permeated through the selectively permeable membrane 116a is discharged into the space 114 outside the fuselage from a pressure reducing valve 110a. 
The conventional air separating section 116 is provided independently of the air cycle cooling device constituting the air conditioner. The air of raised oxygen concentration obtained by separating the nitrogen by means of the air separating section 116 is therefore wasted without being effectively utilized. Furthermore, if both the air cycle cooling device and air separating section 116 are employed in parallel, the engine load is increased due to increase in the amount of air extracted from the engine.
Since the engine output is throttled during the descent of the aircraft, the pressure of extracted air from the engine is lowered. When this extracted air pressure drops, the nitrogen separating ability of the selectively permeable membrane 116a drops. Furthermore, fuel is consumed and the empty volume within the fuel tank becomes large when the aircraft descends after cruising, in which a large amount of nitrogen enriched gas becomes necessary. As a result, supply of the nitrogen-enriched gas required becomes insufficient.
Furthermore, the air supplied into the cabin 108 by the conventional air conditioner is discharged to outside the fuselage. That is, since the internal pressure of the cabin 108 is higher than the pressure outside the fuselage at high altitudes, the air having this pressure difference is wasted without being effectively utilized.
An object of the present invention is to provide an aircraft air conditioner capable of solving these problems.
An aircraft air conditioner according to the present invention wherein air extracted from an engine is cooled by a cooling device and fed into the cabin of the aircraft, comprising: an air separating section having a selectively permeable membrane arranged at a position through which air flowing in an air flow path of the air conditioner passes, so that it separates the air into nitrogen-enriched gas and oxygen-concentrated air, wherein the nitrogen-enriched gas can be fed into a fuel peripheral region of the aircraft, and this oxygen-concentrated air can be fed into the cabin. Preferably there is provided a recirculation air flow path through which air flowing out from the cabin is returned to the cabin, wherein the recirculation air flow path and the air flow path of the extracted air from the engine are connected to each other such that the recirculation air that is returned to the cabin after flowing out from the cabin is mixed with the extracted air, and the mixture of the recirculation air and the extracted air is fed into the air separating section.
According to the present invention, the oxygen-concentrated air from which nitrogen is separated by the air separating section is effectively utilized by being returned to the cabin. Also, when both the cooling device and air separating section are employed at the same time, the engine load can be reduced by restricting the increase of the amount of air extracted from the engine.
Preferably the cooling device comprises a compressor and an expansion turbine, and the mixture of the recirculation air and the extracted air is fed into the air separating section after being compressed by the compressor of the cooling device.
In this way, by utilizing the compressor of the cooling device, the pressure of the mixture of the recirculation air and the extracted air can be raised to the necessary pressure for separating the air constituents by the selectively permeable membrane of the air separating section.
In this case, preferably a normally open air flow path is provided for feeding air from the compressor to the expansion turbine, some of the air flowing through the normally open air flow path is fed into the air separating section through a branching flow path of the normally open flow path, the permeability for oxygen of the selectively permeable membrane is made higher than the permeability for nitrogen thereof, and oxygen-concentrated air passing through the selectively permeable membranes can be introduced into the cabin without passing through the expansion turbine. In this way, oxygen-concentrated air that has been reduced in pressure by passing through the selectively permeable membrane can be introduced into the cabin without passing through the expansion turbine, and air that has passed through the normally open flow path reduces the drop in pressure between the outlet of the compressor and the inlet of the expansion turbine, so lowered efficiency of the air cycle cooling device can be prevented.
Preferably there is provided a compressor for compressing prior to mixing by which the recirculation air is pressurized prior to the mixing with the extracted air. In this way, the recirculation air is pressurized to the same degree as the extracted air pressure prior to the mixing with the extracted air, so that backflow of the recirculation air is prevented and the mixing can be performed smoothly. The selectively permeable membrane of which the permeability for nitrogen is made higher than the permeability for oxygen can be utilized. In this case, preferably the oxygen-concentrated air is expanded by the expansion turbine, and the output of the expansion turbine is employed as power for driving at least one of the cooling device compressor and the compressor for compressing prior to mixing. In this way, the expansion work of the expansion turbine can be effectively utilized.
Furthermore, preferably the air conditioner is provided with an auxiliary extracted air flow path through which the extracted air flows and a changeover valve connected with this auxiliary extracted air flow path and the recirculation air flow path, upstream of the compressor for compressing prior to mixing, wherein the changeover valve is made capable of changing over between a first condition and a second condition, when the changeover valve is in the first condition, the recirculation air is fed to the compressor for compressing prior to mixing and the flow of the extracted air from the auxiliary extracted air flow path to the compressor for compressing prior to mixing is cut off, and when the changeover valve is in the second condition, the extracted air is fed from the auxiliary extracted air flow path to the compressor for compressing prior to mixing and the flow of the recirculation air is cut off. When the changeover valve is in the second condition, the extracted air is compressed by the compressor for compressing prior to mixing instead of the recirculation air and the auxiliary extracted air flow path is connected with the air flow path of the extracted air through the recirculation air flow path. In this way, when the pressure of the extracted air is extremely low, instead of supplying the extracted air directly into the cooling device, the extracted air compressed by the compressor for compressing prior to mixing can be supplied into the cooling device without supplying the recirculation air compressed by the compressor for compressing prior to mixing. In this way, it is desirable to put the changeover valve into the second condition for example in a condition in which the aircraft is descending. Specifically, when the aircraft is descending, the air capacity in the fuel tanks becomes large as a result of the fuel being used up and it is necessary to supply a large amount of nitrogen-enriched gas into the fuel peripheral region because of the increase in air pressure of outside fuselage produced by the descent. Consequently, the air pressure supplied to the cooling device should be a value such as to obtain a sufficient flow rate of nitrogen-enriched gas in the air separating section. As a result, during descent in which the extracted air pressure shows a considerable drop due to throttling of the engine output, it becomes difficult to supply the extracted air directly to the cooling device. Furthermore, during descent, the pressure of the extracted air is still often higher than the pressure of the recirculation air. Consequently, by compressing the extracted air by the compressor for compressing prior to mixing instead of the recirculation air, the energy required for operation of the compressor for compressing prior to mixing can be reduced in an amount corresponding to the difference of the pressure of the extracted air and the recirculation air. The power consumption of the equipment as a whole i.e. the energy consumption can thereby be further reduced.
It is further desirable that the compressor for compressing prior to mixing has a plurality of compression sections, and a mechanism capable of changing over between a condition in which at least two or more of the compression sections are connected in series and a condition in which they are connected in parallel is provided. In this case, preferably the plurality of compression sections are connected in series when the changeover valve is in the first condition and are connected in parallel when the changeover valve is in the second condition. In this way, if the compression ratio in each of the compression section of the compressor for compressing prior to mixing is made practically the same when the changeover valve is in the first condition and when it is in the second condition, the flow rate in the compressor for compressing prior to mixing at the time the changeover valve is in the second condition can be made greater than that at the time the changeover valve is in the first condition by a factor of about the number of the compression sections. In this way, increase in power consumption can be prevented by putting the changeover valve in the second condition in a condition where the aircraft is descending. There is therefore no need to increase the number of the compressor for compressing prior to mixing in order to guarantee the air flow rate when the aircraft is descending. Meanwhile, when the aircraft is descending, high propellant force is not needed and the capacity of the extracted air quantity is increased. Therefore, the second condition does not cause the increase load of the engine.
Preferably, at least one of the cooling device compressor and the compressor for compressing prior to mixing is supplied with at least part of the power necessary for its driving from a motor.
In this way, the difference obtained by subtracting the expansion work of the expansion turbine from the total of the compression work of the cooling device compressor and the compression work of the compressor for compressing prior to mixing can be made up by the power of the motor.
Preferably there is provided a vapor cycle heat exchanger unit of high COP (coefficient of performance) capable of cooling the recirculation air compressed by the compressor for compressing prior to mixing.
In this way, the temperature of the air supplied to the cabin can be suitably regulated with little input energy.
According to the present invention, an aircraft air conditioner can be provided that is capable of contributing to prevention of occurrence of fuel fires and comfort within the cabin is improved, by implementing OBIGGS in a civil aircraft by reducing the size and weight of the equipment, in which the rate and pressure of the air feed into the air separating unit can be guaranteed without increasing engine load.